Ok I think I get it now.

I am going to buy a little filter next week which comes with an air pump. Is an air pump safe? It will help oxygenate the water but it won't negatively affect anything else will it?

Until then every other day I am replacing some of the old dirty water with fresh tap water (boiled then cooled) and scooping out any debris out with the net.

How do I test to make sure the water is getting better? I need some kind of test kit but what am I testing for, amonia?

I definitely think the male is comfortable in the tank as he has been very frisky; following the female around all the time, flicking his anal fin forward and getting really close to her.

Oh and putting the gravel in tonight after it's been thoroughly cleaned.